The present invention relates to a method and apparatus for filtering interference signals in a GPS environment without introducing satellite signal distortion.
GPS (Global Positioning System) is a worldwide satellite-based navigational system consisting of a network of satellites that continuously transmit coded signals. GPS receivers receive and process these coded signals to determine position, velocity, and time. The GPS receivers may be used in many devices such as navigational devices and tracking devices. Although GPS was originally developed for use by the military, its use in commercial applications has increased dramatically over the past few years in areas such as automobile navigation, vehicle location, private and commercial aircraft navigation and landing systems, and surveying and precise timing systems.
Unfortunately, the coded signals transmitted by GPS are susceptible to interference, both unintentional and intentional, due to the low power level of the satellite signals. Unintentional interference may result from cellular phones and television station transmitting antennas. Intentional interference (i.e., jamming) results from signals intentionally produced to interfere with the satellite signals. When interference occurs, the performance of devices that rely on the satellite signals degrade. To maintain or improve the performance of these devices in the presence of interference, GPS receivers must be designed to cancel or minimize the interference.
In conventional multi-channel GPS receivers, channels may be individually filtered and then summed to minimize the effect of interference and to enhance the satellite signal-to-noise ratio. However, these GPS receivers do not guarantee the integrity of the frequency components of the satellite signal and can result in degraded GPS performance even when the interference is cancelled. Accordingly, there is a need to minimize interference effects while minimizing or eliminating satellite signal distortion.
There is provided a method for minimizing an effect of at least one interference signal while minimizing the distortion of at least one GPS satellite signal. The method comprises receiving the at least one interference signal and the at least one GPS satellite signal by a plurality of antenna elements and processing the received signals. The method further comprises filtering the received processed signals by a plurality of multiple tapped delay line structures based a plurality of filter coefficients. Still further, the method comprises determining the plurality of filter coefficients such that the plurality of filter coefficients equals R{tilde over (xx)}xe2x88x921C[CHR{tilde over (xx)}xe2x88x921C]xe2x88x921F wherein CH{tilde over (w)}=F, where {tilde over (w)} equals the plurality of filter coefficients, R{tilde over (xx)} equals a covariance matrix, and C and F are determined to preserve a frequency spectrum of the at least one GPS satellite signal.
Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.